Natural and synthetic anionic saccharide-based compounds continue to be used, and developed for use, as therapeutics. A well known example of such a compound is the natural product heparin which has been used clinically for over 80 years as an anticoagulant. Heparin has undergone two generations of improvements resulting in products with greater selectivity and/or specificity for the target. The first was a semi-synthetic process which generated a low molecular weight heparin displaying a greater specificity of action. The second approach involved a synthetic pentasaccharide which was selective for the target protein. The synthetic approach, however, consisted of approximately 40 chemical steps, highlighting the technical difficulty associated with the synthesis of such compounds.
One approach to overcoming the challenges posed by the synthesis of heparin, and GAGs more broadly, has been to target GAG mimetics. One class of such mimetics is the semi-synthetic sulfated natural homo-oligosaccharides. There is, however, disparity between the small size of the oligosaccharides that are readily accessed from natural sources and the independently selected from maltotriose, maltotetraose, maltopentaose, xylotetraose, xylopentaose, chitotetraose and chitopentaose which each comprise at least one anionic substituent such as a sulfate or phosphate substituent.
In another aspect the invention provides a process for preparing an anionic oligosaccharide of formula (I):
wherein:                S1 and S2 each independently represent anionic oligosaccharides;        x1 represents an integer from 1 to 4;        x2 represents an integer from 0 to 11;        x3 represents an integer from 0 to 10;        x4 represents 0 or 1; and        x5 represents an integer from 1 to 4,the process comprising the steps of:        a) transforming each of the oligosaccharides into anionic oligosaccharides; and        b) conjugating the oligosaccharides;wherein steps a) and b) may be performed in either order.        
In another aspect the invention provides the use of an anionic oligosaccharide of formula (I):
wherein:                S1 and S2 each independently represent anionic oligosaccharides;        x1 represents an integer from 1 to 4;        x2 represents an integer from 0 to 11;        x3 represents an integer from 0 to 10;larger oligo- and polysaccharides which produce activity in many biological systems. In particular, access to oligosaccharides comprising 6 or more monosaccharides, whilst maintaining the goals of structural diversity and low cost, is especially difficult.        
There remains a continuing need to produce GAG mimetics which display a high degree of selectivity and/or specificity, and which are able to be produced by simple, cost effective methods.